Fast pyrolysis is a process during which organic carbonaceous biomass feedstock, i.e., “biomass,” such as wood waste, short rotation crops, agricultural waste, municipal solid waste, energy grasses, algae, etc., is rapidly heated to between about 300° C. to about 900° C. in the absence of air using a pyrolysis reactor. Under these conditions, solid products, liquid products, and gaseous pyrolysis products are produced. A condensable portion (vapors) of the gaseous pyrolysis products is condensed into biomass-derived pyrolysis oil (also referred to as “pyoil”). Biomass-derived pyrolysis oil can be burned directly as fuel for certain boiler and furnace applications, and can also serve as a potential feedstock in catalytic processes for the production of transportation fuels and transportation fuel blends in petroleum refineries. Recent estimates indicated that deoxygenated liquids produced from biomass-derived pyrolysis oil have the potential to replace more than 50% of transportation fuels, thereby reducing the dependency on conventional petroleum and reducing transportation sector environmental impacts such as greenhouse gas (GHG) emissions.
However, biomass-derived pyrolysis oil is a complex, highly oxygenated organic liquid having properties that currently limit its utilization as a biofuel. For example, biomass-derived pyrolysis oil has high acidity and a low energy density attributable in part to oxygenated hydrocarbons (and water) in the oil. “Oxygenated hydrocarbons” as used herein are organic compounds comprising hydrogen, carbon, and oxygen. Such oxygenated hydrocarbons in the biomass-derived pyrolysis oil include carboxylic acids, phenols, cresols, alcohols, aldehydes, etc. some of which are chemically unstable and can undergo secondary reactions during storage. Conventional biomass-derived pyrolysis oil comprises about 30% or greater by weight oxygen from these oxygenated hydrocarbons. Conversion of biomass-derived pyrolysis oil into high energy density, drop-in biofuels and chemicals requires hydrogen addition and full or partial deoxygenation of the biomass-derived pyrolysis oil.
Unfortunately, biomass-derived pyrolysis oil is a difficult feedstock to hydroprocess. First, catalytic hydrodeoxygenation of biomass-derived pyrolysis oil is very exothermic and can lead to undesirable hotspots anywhere from the catalyst surface to throughout the hydroprocessing reactor, making it difficult to control the reactor temperature profile both axially and radially. Poorly controlled catalytic deoxygenation of biomass-derived pyrolysis oil typically leads to fouling of the catalyst and rapid plugging of the hydroprocessing reactor. Without proper control of the reaction temperature, concentrations of the reactive species, and catalyst composition, refractory components can form on the catalyst surface and in the interstitial space between catalyst particles creating undesirable flow patterns, loss of catalyst activity, and a build-up in reactor differential pressure. It is believed that the formation of refractory components is due to thermal or acid catalyzed polymerization of at least a portion of the hydrogen-deficient and chemically unstable components present in the biomass-derived pyrolysis oil, e.g., second order reactions in which at least a portion of these reactive species chemically interact creating either a glassy brown polymer or powdery brown char that limits run duration and processibility of the biomass-derived pyrolysis oil.
Accordingly, it is desirable to provide apparatuses and methods for producing a low-oxygen biomass-derived pyrolysis oil with improved control over the reaction conditions. Moreover, it is desirable to provide apparatuses and methods for producing a low-oxygen biomass-derived pyrolysis oil with improved catalyst stability and increased on-stream efficiency and to improve the overall efficiency of converting biomass-derived pyrolysis oil to higher energy density liquid products suitable for use as transportation fuels and blendstocks. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.